An increasing number of births are planned, either by inducing labour or by planned caesarean. Giving birth early carries long-term as well as short-term risks. The final weeks of pregnancy are crucial for optimal brain development (the brain weighs two-thirds at 34 weeks of what it will weigh at 40 weeks). It is in the final weeks of development that many finer brain networks linked to developmental outcome are formed. A growing body of evidence points to long-term developmental delay by the time induced premature children reach school. Additionally, every week a baby is born prior to 39 weeks increases the likelihood of the need for breathing support and admission to newborn intensive care. This is important as these babies occupy scarce resources that could be avoided if birth could be safely delayed by a week.
For many years, we have assumed babies born after 37 weeks gestation have no risk of problems. After all, the official definition of “term” has been classified as the period between 37 and 42 weeks of pregnancy. However, there is no scientific basis for 37 weeks being recognized as the time when a baby is mature.
The rise in early planned birth is a result of both planned interventions because of concerns over the mother’s and/or baby’s welfare or, less commonly, for convenience. Factors that have contributed to planned early births on health grounds have included increased ultrasound surveillance in pregnancy, which has increased the detection of babies who are small for their gestational age. The lack of sufficiently accurate tests to distinguish a healthy small baby from a small one that is compromised means these babies can be delivered early in the belief this is a safer option. Another factor is that diabetes in pregnancy is more common, which can lead to problems at birth, such as the baby being very large or suffering from respiratory distress, or for the mother, such as high blood pressure and preeclampsia. So 37 weeks, or term, has become an accepted time for planned birth for these babies. Planning to give birth early occurs in the belief that early delivery carries no significant risk to the baby or is safer for the mother and/or baby compared with continuing the pregnancy. Widely held views that it is safe for the baby to be born a few weeks early may lead to a decision for elective early birth for no medical reasons.
In Australia, since the 1990s there has been a major change in birth practices that has resulted in a silent but steady shift towards women giving birth before 40 weeks. In New South Wales, for example, in the mid 90s a woman was most likely to deliver at 40 weeks. In 2016, between 38 and 39 weeks is the most common. During that time there was a year-on-year increase in the number of births between 34 to 39 weeks to the point where nearly one in five of all single babies born was at 38 weeks, one in 15 at 37 weeks and one in 40 at 36 weeks.
For every week a child is born earlier than 39 weeks there is a small but significant increase in the likelihood of them being developmentally vulnerable. Australian kindergarten children born after a planned birth scored poorly on two or more of these categories: physical health and well-being, social competence, emotional maturity, language and cognitive skills, communication skills and general knowledge. These are associated with longer term health, education and social outcomes. The risk was higher for babies born after a planned birth compared with spontaneous birth.